1. Field of the Invention
The present invention relates to a tilt sensor which detects the tilt angle of vehicles and industrial machines.
2. Description of the Related Art
In recent years, air bags which inflate in accidents such as head-on and side collisions have been widely used as a safety mechanism for vehicles. In such an accident, a vehicle may roll over. Therefore, a tilt sensor which detects such rolling movements and operates the safety mechanism can be effective.
A conventional tilt sensor is disclosed in the Japanese Laid-open Patent No. S60-154108. FIG. 21 shows a construction of a conventional tilt sensor. An angle of a plate-type pendulum 101 relative to substrate 102 changes according to tilt angle of a vehicle. Tilt angle is detected by sensing whether or not light passes through a optical interrupter 104 facing slits provided around the periphery of the pendulum 101. On the surfaces of the substrate 102 is magnet 103. The pendulum 101 turns in a direction transverse to the magnetic flux of the magnet 103. When the pendulum 101 turns at a speed of V, an eddy current is generated by an electromotive force in a direction perpendicular to the rotation direction of the pendulum 101. The eddy current applies a force relative to the speed of V to the pendulum 101 in a direction opposite to its rotation direction. This force functions as a braking force and stabilizes the rotation of the pendulum 101.
The tilt sensors installed in vehicles such as a car needs to be able to switch on and off an electric current of almost 10A flowing in an inflator in order to detect dangerous tilt angle of a car which result in a rollover and to inflate a side air bag. Since the tilt sensors are installed inside a control unit, they need to be compact, and rotate smoothly without being unduly affected by external vibrations.
The foregoing conventional tilt sensor, however, requires amplification of detected signal because the level of detected signal is low. Thus, it requires more printed circuit boards to amplify the signal, resulting in lower reliability. Moreover, its rotation tends to be affected by the diameter of the rotation shaft and the center of the gravity of the pendulum. Furthermore, an optical interrupter needs to be disposed around the periphery of the pendulum. These structural limitations has restricted further down-sizing and reduction in height.
The present invention aims at providing a more compact and reliable tilt sensor which can be installed in vehicles to solve the foregoing problems.
The tilt sensor of the present invention comprises the following elements:
(a) a base mounted on a fixed body;
(b) a pair of supporting members disposed on the base;
(c) a pendulum assembly;
(d) an eddy current brake fixed to the base; and
(e) reed switches fixed to the base at the location outside the rotation trail of the pendulum assembly.
The pendulum assembly comprises the following elements:
(a) a rotatable pendulum made with non-magnetic material, integrally formed with a rotation shaft which is supported in between the pair of supporting members;
(b) magnetic flux generating means fixed in the vicinity of the periphery of the pendulum, and the direction of whose magnetic poles is parallel to the rotation shaft; and
(c) a yoke approximately U-shaped, fixed to the pendulum. Either end of the U-shape yoke faces a magnetic pole of the magnetic flux, generating means. The reed switches open and close based on the magnetic flux generated by the magnetic flux generating means which operates according to the rotation of the pendulum assembly.